Since fossil fuel, which is the material humans depend on to obtain energy, might be drained out in the twenty-first century, and leads to the increased price of fossil fuel. Therefore, every country takes efforts on developing new energy resources in the recent years, including solar energy, wind power, water power, biomass power and newly-explored fossil fuel storage sources, etc. Among these, solar energy which is radiated from the sun is deemed as the clear energy without generating greenhouse gases or aggravating the greenhouse effect, and has great benefit on resolving the energy requirement and decreasing carbon dioxide emission.
The present solar cells apply various materials, including single crystalline silicon, polycrystalline silicon and amorphous silicon, to form solar cells. Among these, the polycrystalline silicon is composed of numerous different single crystalline silicons separated by grain boundaries. Due to the mechanical properties of polycrystal, the cutting and manufacturing procedures of the polycrystalline silicon are more difficult than those of the single crystalline silicon and the amorphous silicon. The efficiency of the polycrystalline silicon solar cell is lower than that of single crystalline silicon solar cell, and the polycrystalline silicon is suitable for the low-efficient electrical power application system. In addition to adapting the silicon material, other semiconductor materials can be adapted to manufacture the solar cell, such as cadmium telluride (CdTe), gallium arsenide (GaAs), indium gallium arsenide (InGaAs) or other III-V group compounds.
All the present solar cell research fellows devote to improve the photoelectric conversion efficiency of the solar cells. For instance, the electrode is manufactured as the finger-shaped, for increasing the incident light area ratio; the surface of the solar cell is manufactured as the pyramid structure and the anti-refection layer is added, for increasing the light trapping and reducing the light reflection; the metal electrode is buried into the substrate for decreasing the series resistance; and the electrodes of the solar cell are manufactured on the identical surface to form the point-connected solar cell, for increasing the incident area and welding easily. The above-mentioned manufacturing processes for the solar cell efficiency improvement mostly arise the photoelectric conversion efficiency by refining the solar cell structure.
In addition, there are solar cells efficiency improvement made by using the lamination of the amorphous silicon thin layer and the microcrystalline silicon thin layer. However, since taking the electron-hole pairs to the electrodes uneasily and un-effectively, and the narrower absorbable wavelength range, it results in the ineffective conversion efficiency improvement of the amorphous silicon thin layer.
Therefore, how to increase fewer cost or not to complicate the manufacturing process, and the photoelectric conversion efficiency of the solar cell is increased are extremely important.
It is therefore attempted by the applicant to deal with the above situation encountered in the prior art.